This invention relates to a wiring board, particularly a high-density wiring board suited for the realization of "chip-on-board" technology, and a process for producing the same.
The high-degree integration of LSI chips and speed-up of operation has intensified the necessity of higher wiring density, lower dielectric constant, etc., on the part of wiring board. Especially, request is keen recently for the fruition of chip-on-board system in which the bare chips are mounted directly on a substrate for reducing the chip-to-chip wiring length. For the production of wiring boards adaptable to such chip-on-board system by using an uncostly and mass-produceable plastic insulating substrate, researches have been made on the method in which, for enabling higher density of signal wiring and high-speed operation, the insulating layers made of a polyimide resin and the copper-based thin-film wiring layers formed by vacuum deposition or other techniques are built up successively on the wiring pattern side of a single-side copper-clad laminate on which the necessary wiring pattern including power source, grounding layer, etc., has already been formed on one side thereof.
However, the following problem was involved in forming said thin-film wiring layer on the copper-clad laminate.
In case of using a glass cloth-epoxy laminate or glass cloth-polyimide laminate which are the typical examples of copper-clad laminates, since water is adsorbed on the glass cloth, such water would be gasified in treatment under vacuum (reduced pressure) which is required for vacuum deposition or sputtering, causing exfoliation at the interface between the glass cloth and the resin. It was therefore difficult to form a thin-film wiring pattern on a practical copper-clad laminate by a vacuum process.